Hypoxia and hepatic coma are common clinical conditions. In these studies we will seek to develop strategies to improve cerebral oxygenation by manipulation the oxygen-hemoglobin dissociation curve, a curve controlled in part by the concentration of 2,3-diphosphoglycerate. Hepatic coma is the result of the combined action of various toxins, including ammonia and short-chain fatty acids (SCFA). We will study ammonia metabolism by using N-13 ammonia and a mathematical model of its metabolism. Factors influencing SCFA uptake by the brain will be studied using C-11 acids. The pharmaceuticals and techniques will be directly applicable to studies of humans using positron-emission tomography.